1. Field of the Invention
The present invention relates to a camera provided with a open/close type barrier mechanism which protects the lens front of a lens barrel and an optical apparatus.
2. Description of the Related Art
There are proposals of various types of a barrier mechanism which is provided in front of an image-pickup lens of a camera and causes barrier blades to perform an open/close operation in conjunction with operations (protruding and retracting) of the lens barrel in the direction of the optical axis. A basic structure of the barrier mechanism is shown in FIG. 4.
Two barrier blades 101 are supported by rotation shafts 102 in a rotatable manner through engagement of hole portions 101a with the rotation shafts 102. The rotation shafts 102 are provided on a base plate (not shown) (e.g., lens barrel, etc.). Then, driving pins 101b engage with notch portions 103a of a first driving ring 103.
The first driving ring 103 engages with a second driving ring 104 in a rotatable manner and is energized by an absorption spring 105 with respect to the second driving ring 104 in the direction indicated by arrow A (one turn direction). Here, since a hooking shaft 103b normally contacts a stopper 104a of the second driving ring 104 by spring force of the spring 105, the first driving ring 103 normally operates together with the second driving ring 104 as one unit.
The second driving ring 104 is held by a base plate (not shown) (e.g., lens barrel, etc.) in a rotatable manner and energized by an opening spring 106 in the direction indicated by arrow B.
One end of the opening spring 106 is fixed to a hooking shaft 107 and the hooking shaft 107 is provided on a base plate (not shown) (e.g., lens barrel, etc.). The first driving ring 103 and second driving ring 104 are rotated by the opening spring 106 in the direction indicated by arrow B and cause the barrier blades 101 to rotate in the opening direction (direction indicated by arrow C) as a result. Since the barrier mechanism is held by a base plate (not shown) (e.g., lens barrel, etc.), the barrier blades 101 are in an open state when the lens barrel protrudes and it is an image-pickup state. On the other hand, when the lens barrel retracts and it is in a non-image-pickup state, a cam face 104b of the second driving ring 104 contacts a cam-shaped protrusion 108 inside the camera and moves along the cam-shaped protrusion 108 and thereby causes the first driving ring 103 and second driving ring 104 to rotate in the direction indicated by arrow A. In this way, the barrier blades 101 rotate in the direction opposite to the direction indicated by arrow C to close the lens front.
When an external force in the direction indicated by arrow C is applied to the barrier blades 101 which are in a closed state, only the first driving ring 103 rotates in the direction indicated by arrow B against the spring force of the absorption spring 105.
In the above described structure, the structure in which the base plate and lens barrel house and hold the barrier mechanism will be explained using the cross-sectional views shown in FIG. 5 to FIG. 7. In these figures, the same members as those explained in FIG. 4 are assigned the same reference numerals.
In the structure shown in FIG. 5 (first conventional example), as disclosed in Japanese Patent Application Laid-Open No. H8 (1996)-234292 and Japanese Patent Application Laid-Open No. H10 (1998)-186453, the rotation shaft 102 and hooking shaft 107 (not shown) are directly provided in the lens barrel 109. Furthermore, the barrier mechanism is housed in the lens barrel 109 and a barrier cover 110 covers the front of the lens barrel 109.
The structure shown in FIG. 5 is simple and allows the barrier mechanism to be assembled from the front of the lens barrel 109.
The structure shown in FIG. 6 (second conventional example), as is disclosed in Japanese Patent Application Laid-Open No. H9 (1997)-211536 (corresponding to U.S. Pat. No. 5,862,426 and EP 0 788 020 A1), is constructed in such a way that the barrier driving mechanism other than the barrier blade 101 is assembled from the inner side (right side in FIG. 6) of the lens barrel 109. In this structure, a plate 112 is used to house the first driving ring 103 and second driving ring 104 within the lens barrel 109.
The structure shown in FIG. 7 (third conventional example) is a structure in which the barrier blades 101 and barrier driving mechanism are separated by a barrier base plate 113. Thus, the rotation shaft 102 is provided on a barrier base plate 113.
However, in the structure shown in FIG. 5, when the barrier blades 101 moves to the closing position, the second driving ring 104 may be pushed forward (left side in FIG. 5) in the lens barrel 109 by the cam-shaped protrusion 108, thereby preventing the movement of the barrier blades 101 and producing insufficient closing of the barrier blades 101.
On the other hand, in the structure shown in FIG. 6, since the part of the lens barrel 109 is located between the barrier blades 101 and barrier driving mechanism (especially, second driving ring 104) other than the barrier blades 101, even if the second driving ring 104 is pushed forward in the lens barrel 109 by the cam-shaped protrusion 108 as described above, the second driving ring 104 does not prevent the movement of the barrier blades 101.
However, since the barrier driving mechanism needs to be assembled from the inner side of the lens barrel 109 (right side in FIG. 6), it is difficult to imbed the barrier mechanism in the lens barrel 109.
In the structure shown in FIG. 7, since the barrier base plate 113 is placed between the barrier blades 101 and barrier driving mechanism (especially, the second driving ring 104), even if the second driving ring 104 is pushed in by the cam-shaped protrusion 108 as described above, the movement of the barrier blades 101 is not blocked. Moreover, the barrier mechanism can be assembled from the front side (left side in FIG. 7) of the lens barrel 109, and therefore it is also easy to imbed the barrier mechanism in the lens barrel 109.
However, the structure shown in FIG. 7 may make the open state and closed state of the barrier blades 101 unstable.
That is, the closed state and open state of the barrier blades 101 are affected by the relative positional relationship between the rotation shaft 102 and driving pin 101b, but if the rotation shaft 102 is provided on the barrier base plate 113, the barrier base plate 113 moves within the plane orthogonal to the optical axis due to backlash of engagement between the lens barrel 109 and barrier base plate 113, assembly error, part variations, etc., also causing the position of the rotation shaft 102 to change.
Thus, when the position of the rotation shaft 102 changes, the relative positional relationship between the rotation shaft 102 and driving pin 101b is not constant and the opening position and the closing position of the barrier blades 101 are not fixed to a predetermined position, and therefore the open state and the closed state of the barrier blades 101 become unstable.